DESCRIPTION (Adapted from abstract): Bacteriorhodopsin is a light-driven proton pump that has several well-characterized intermediates in its photocycle. The general aim of this proposal is to define the mechanism of proton transport in bacteriorhodopsin by mapping the conformational changes during the photocycle in atomic detail. The specific aims are 1) to determine the high resolution structure of light-adapted (ground state) bacteriorhodopsin, 2) determine the structure of the M intermediate by solving the structure of D96N bacteriorhodopsin 3) determine the crystal structure of the K intermediate, 4) solve the crystal structure of the L intermediate and 5) solve the structure of a chloride pump, either halorhodopsin, or D85S bacteriorhodopsin, which functions as a chloride pump.